text:
Why does a rocket engine increase power with speed if the burn rate is constant?
A rocket produces constant thrust with speed, and that means increasing power with speed.
Where does this increase in power come from if the fuel burn rate is constant? How can we explain this in the reference frame of the rocket without violating the laws of physics?
Does a turbo fan and turbo jet also produce constant thrust with speed?

"Rocket produce constant thrust with speed,that mean increase power with speed."  I think you have a real need for evidence to support this claim.  Acceleration increases as the rocket burns, because the mass of fuel it's accelerating decreases.  Many launch vehicles (especially human-carrying ones) actually reduce their power/thrust in order to keep acceleration within tolerable limits.  See the answer here: https://space.stackexchange.com/questions/7829/launch-accelerations-values-history

I would have expected such a question on Space Exploration. Its "Rockets" tag has 1055 questions.

"A rocket produces constant thrust with speed, and that means increasing power with speed." Not correct. Rocket thrust is not related to the speed of the rocket, only to the propellant consumed. Jets and props push against the air around them to gain thrust, rockets do not.

@PaulSmith -- re" Rocket thrust is not related to the speed of the rocket," -- that's exactly what Jurgen said, that's the whole premise of the question.

@quietflyer - "...that means increase power with speed" - no, it doesn't. The thrust of the rocket has nothing to do with its speed so there is no relationship between its speed and power.

Cool that this question was asked on the very day I happened to watch October Sky.

@PaulSmith - Power = Force * Speed, therefore if thrust (force) is constant, there is certainly a relationship between speed and and power.  Even if thrust is not exactly constant, increasing speed is very strongly correlated to increasing power.

@quietflyer - power = the force of the exhaust * the speed of the exhaust vs the rocket,  not the speed of the rocket vs the air.

@PaulSmith -- I think you are mistaken.  Simply consider the case of a jet airplane.  To a first approximation for a given fuel flow thrust is constant, and power therefore becomes higher and higher as the aircraft flies faster and faster.  Very different from the case of a piston engine, where to a first approximation power is constant for a given fuel flow, and thrust therefore must drop off as airspeed increases.  And that's why the output of a piston engine is typically expressed in terms of horsepower, while the output of jet engine is typically expressed in terms of pounds of thrust.

@PaulSmith -- the rocket case is rather similar to the jet case-- and very different from the piston-engine case.  All based on the relationship that power = force times speed, where "speed" is the speed of the vehicle-- not the exhaust stream.

Put simply, the variation in power is due to the distinction between the exhaust jet power and mechanical power added to the vehicle.
The power of the exhaust gas stream measured in the rocket-fixed reference frame is only dependent on the rate of energy release by the propellant.
The rate of kinetic energy addition to the vehicle depends on the thrust developed by the engine and the velocity of the vehicle measured in some other reference frame.
These two powers will only match momentarily when the vehicle velocity equals the exhaust velocity (when the exhaust is left at rest).
Intuitively you could say something like this:
When the rocket is moving slower than its own exhaust velocity, the power deficit (exhaust power - vehicle power) ends up as residual kinetic energy in the exhaust.
When the rocket is moving faster than its own exhaust velocity, the power excess comes from the kinetic energy present in the propellant.
Here is a plot of total system energy for a rocket of mass ratio 5 accelerating from rest. The kinetic energies of the rocket structure, onboard propellant, and exhaust gases as well as the internal (chemical) energy of the propellant are shown, just to demonstrate the total remains constant regardless of how much fuel has been burned.

"When the rocket is moving faster than its own exhaust velocity.." How on earth (or in space) can it do so?

@Jpe61 it's basically like using a catapult to take off from an aircraft carrier that has just stopped is engines and is still drifting forwards. Despite accelerating the plane to much higher speed than the carrier could ever make, the carrier is still going forward in the end. — The trick is to push yourself off a reaction mass that's bigger than yourself. In a rocket, that mass is the fuel.

Yea did some quick reading on this. Oh boy, talk about something being counterintuitive!

Power = Work/time = Force × distance/time = mass × acceleration × Velocity
We must remember these definitions were created for draft horses before the age where aerodynamic drag was significant.
"Power" more accurately describes the Energy state of an object.
In a vacuum, away from a gravitational field, a rocket under constant thrust force will have more and more power (as an impactor) as its speed increases.
A turbofan and turbojet, operating in the atmosphere, are limited in the amount of thrust they produce by oxygen available and limited in velocity by drag.  In extreme cases (such as hypersonic flight), friction heating from drag also plays a significant role.
Turbofans generally operate subsonicly for greater fuel efficiency.
"Power" vs drag graphs are popular for aviation training programs, but can be confusing unless Power = Thrust x Velocity is applied.
Thrust is an easier way to quantify engine output. Even for propeller driven aircraft, "horsepower" can be described as torque at a given rpm.

"'Power' more accurately describes the Energy state of an object", power is a rate not a state, the rate at which energy is (can be) transferred.

@mins well, you see that's where the confusion lies.  Velocity is a state, rate of energy input (fuel burn, thrust) can be constant, but velocity is determined (initially) by time, later by drag.

@mins but your statement is not incorrect as (working through units) power input (fuel burn) can be described as mv$^2$/time.

"In a vacuum, away from a gravitational field, a rocket under constant thrust force will have more and more power (as an impactor) as its speed increases." - from this we deduce that it gets very difficult to make a rocket that can keep applying a high constant acceleration over a very long time period. All the energy in the impactor was originally chemical energy in the fuel. You don't get anything for free, even in space. The difficulty in making a long-burn rocket is that if you add fuel to make a longer burn time, the rocket's initial weight is higher, so it initially accelerates slower.

"All the energy in the impactor was originally chemical energy in the fuel (and oxidizer)"  Yes, this is what BowlOfRed pointed out.  In aviation, we wind up burning fuel against drag, part of drag makes lift.  Fortunately, there is enough O2 for combustion, (solar electrics are making it on Mars).

Rocket produce constant thrust with speed,that mean increase power with speed.

If you limit "power" to mean the change in energy over time of the vehicle + unburned fuel, then yes, that's correct.

Where this increase in power come from if fuel burn rate is constant,how explain this in reference frame of rocket without violate physics laws?

It comes from only looking at part of what the engine is doing.  The other change the engine makes is a change in energy of the fuel/exhaust.
At the first instant that the engine is running (when the rocket is still stationary), 100% of the combustive power of the engine goes into accelerating the fuel into exhaust.  The power going into the vehicle is zero, but the engine is still doing something.
As the rocket accelerates in that frame, we see the ratio of where the power goes changes.  More power goes into accelerating the vehicle and less power goes into accelerating the exhaust.
If we assume the engine is running with nearly constant fuel flow, then we would see at any instant
$$\Delta E_{\text{combustion}} = \Delta E_{\text{rocket}} + \Delta E_{\text{fuel}}$$
As it accelerates away, the amount going into the rocket term is increasing while the amount going into the fuel term is decreasing. (And in fact that final term can become negative so that the energy going to the rocket is greater than the energy from combustion).

Does turbo fan and turbo jet also produce constant thrust with speed?

That's a useful approximation over a large range of operating conditions.  But unlike a rocket, airplanes have increasing drag forces as they accelerate.  This limits the top speed and the acceleration possible.  Since most airplanes fly with a cruise (non-accelerating) portion dominating, the idea of how the KE of the airframe changes over time is much less interesting.

a thoughtful answer but ... from the rocket reference frame isn't exhaust velocity always the same?  Isn't that force always accelerating the rocket?  That is the "power" quandary.  As the rocket speeds up, it by definition P= Fxv, it has more power.

In the rocket reference frame, 100% of combustion goes into a constant speed exhaust.  There is no change in power that I see.


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How can I find telephone numbers for FAA ATC facilities?
It is often desirable to call an FAA air traffic control (ATC) facility on the telephone:

To ask a question about a "mark-the-tape" incident
To request a tour
To notify the facility of unregulated nearby operations like RC plane flying

How can one find the non-emergency telephone number for an ARTCC, TRACON, or control tower (ATCT)?

in a mark-the-tape incident, they'll probably give it to you over the air.

also note that not all ATC facilities in the US are FAA, some are contract towers.

@falstro Not if you (the pilot) are the one requesting the tape be marked. And yes, information on locating contact information for contract towers would be useful too. (Hint: FSS can give you that info whether it's a contract tower or not.)

Might be, the only occasion I've witnessed (LiveATC) the tower asked if he wanted a number to call when he asked them to mark the tape. YMMV of course, but they'll probably give it to you if you ask for it, as it is usually easier to deal with it over the phone than to duke it out over the air :)

You would think the control tower phone numbers would be listed prominently and conveniently on the FAA website.
You would however be wrong1.
Your best bet would be to contact the Flight Standards District Office that covers your area - they can get you in touch with whatever other branches of the FAA you might need to talk to. You can also get tower phone numbers from Flight Service (1-800-WX-BRIEF).
AC-U-KWIK also has tower phone numbers in a conveniently searchable system (punch in the airport identifier and it will be in the results you get), and the printed edition of the AOPA airport directory used to have tower numbers as an appendix (I'm pretty sure it still does).

1 – Actually that's not strictly correct: some regions publish tower numbers prominently. Most don't, or my search skills aren't good enough to find them.

The A/FD is available in a searchable digital format here http://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dafd/ and should contain all information found in the printed AFD.  Note that there may be delays in publishing the most recent directories.

@DavidWilkins does the A/FD have tower phone numbers? I remember looking for this info a while ago and not finding it in there...

I don't know about the Tower/TRACON, but if you look under facilities, you should be able to find an Airways/Facilities number which is always an FAA number.  From there, they should be able to direct you to the proper place.

If it's a controlled airport you can probably get it from the airport managers office as well.

+1 for AC-U-KWIK. I just looked up my facility and can confirm that the listed phone number will actually ring the phone in the tower (not the recorded line, but the phone in the back).

Near the end of the Chart Supplement there is a list of ARTCCs and airports with 24 hour phone numbers.
The Chart Supplement also has the number for the Airport Manager for every airport. They should be able to get you in touch with the tower if it is not on the list.
You can download these pages in ForeFlight or directly from the FAA website.

For the U.S.:
AIR TRAFFIC CONTROL TOWER (ATCT),
TERMINAL RADAR APPROACH CONTROL (TRACON),
AND AIR ROUTE TRAFFIC CONTROL CENTER (ARTCC)
TELEPHONE NUMBERS AND LOCATIONS
http://www.csobeech.com/files/ATC-Phone-Numbers.pdf

Welcome to aviation.SE! The document you linked to is over 10 years old: it's from 2005/2006. Do you have a current version, and preferably from an official source, i.e. the FAA themselves?

That looks like a great link, except that it is so outdated.

The FAA digital products page that JScarry linked to needs some explanation of how to find the phone numbers. It took me a while to find where the phone numbers are located. Go to the Browse Airports/NAVAIDs map, select your region or state. In the Search Results table, select a "NC" link in "Vol / Back Pages" column. The entire 171 page PDF will be downloaded. Around page 17 is the list of TRACONS, towers and ARTCCs and their phone numbers. They certainly hid the phone numbers well.
Here is another website that appears to be current, but not as detailed as the official FAA document: 123ATC.com It seems to be geared towards a career as a controller.

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Why is the autopilot called "George?"
The autopilot of an airplane is frequently referred to as "George" (for example, in this answer). When did this nickname enter common usage, and what is its origin? Please cite sources if possible!

The first "practical" autopilot was invented by George DeBeeson (the patent can be found here, updated here) - This seems to be the most likely reason for the informal name "George" for the autopilot system on aircraft.
Autopilots are also sometimes called "Otto" (as in Otto the Autopilot from Airplane!, and our very own chat bot, but this seems to be less common than "George".

Don't forget Otto from Wall-E ! (Actually it could be "Auto" there, but to me they sound just about the same.)

Audible warning systems are often called "Bitchin' Betty@.

It is my understanding that the Pullman railcar of America ran an advert at the turn oh the 19 century  "let George do it"
Source: https://h2g2.com/edited_entry/A87996172

Welcome to the site! Do you have any source that links that to aviation?

The term "George" as a reference to autopilots originated in the RAF in WWII.  It is a reference to the aircraft's "owner" King George.  Also, at the time, there was a popular radio show referenced in an earlier answer that may have reinforced the use of "George". I have spoken to a number of British WWII pilots. Everyone assumed it was a reference to King George.  None of these pilots were aware of the name of the inventor of the earliest autopilot.  They were, however, aware of the name Sperry.

You should provide links and references to improve your answer.

Who is “Sperry” and why is that relevant?

Perhaps from the Old Tyme Radio Show "Let George Do It!" wherein the hero hired himself out to do jobs too tough for his customers.

This answer appears to be little more than speculation. Are there any references you can cite which would support your proposed answer?

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What materials make up most of the weight of an aircraft?
What are the material types account for most of the empty weight of an airplane (Boeing 747), besides aluminum or its alloys used in fuselage?

I would think the engines are rather beefy, but since you specifically mention aluminum are you looking for a breakdown by material type, or are actually looking for components, like 'engine', 'wing', 'landing gear'?

I am looking for breakdown by material type

On a lot of large aircraft, the answer would be fuel. (I realize that's not what you're asking)

Besides aluminum alloys, most of an airplane's weight is steel, titanium, and composites. Here is a chart comparing the 747 and 777 structural weight, with a breakdown typical for similar airliners:

Source
Steel is used in components where strength or part life is most important, like landing gear and other important structural elements, as well as many fasteners. Titanium is used where weight and high temperature are important, such as around the engines. Composites are traditionally used for many less-structural applications such as panels and fairings, but may also be used in the empennage (tail surfaces) or on the interior as floor beams. Other materials will include alloys like nickel, as well as specialty materials like rubber, plastic, and fabric, which are used mostly in the cabin.
New aircraft like the 787 and A350 use composites much more extensively, replacing much of the aluminum. Titanium is also used more in these aircraft because it does not tend to corrode in contact with carbon fiber composite like aluminum does.

Source
Federico pointed out that the two graphics differ in the amount of aluminum on the 777 (70% on the first vs. 50% on the second), because the first chart shows only structural weight, while the second is overall.

I note that the 777 stats differ significantly between your top right pie chart and the lower right "By comparison" text inset.

@Timbo Yes, I'm not sure why that is.

because the first image caption says "structural materials mass distribution", I the understand that all non-structural components (e.g., wing surfaces) are not included

@Federico good observation, but I'm not quite convinced that the 777 has 11% weight in structural composites.

http://www.nap.edu/openbook.php?record_id=11424&page=12 and here: http://www.dailyreckoning.com.au/asiana-boeing-777-lifesaving-defence-tech-miracle-materials-in-action/2013/07/10/ "The cabin floor and floor supports, as well as vertical fin and horizontal stabilizers in the rear, are made out of carbon-fiber reinforced plastic."

@Federico thanks, you're right, I will include that info.

"Steel is used in components where strength is most important" - it's not strength but resilience/toughness. In particular, aluminium suffers from fatigue. Steel may deform more, but it will be elastic. Consider the landing gear: you don't care if it bends 10 mm on each landing, if it bends back after takeoff. But any permanent bend, even just 1 mm on per landing would be a problem.

A general breakdown by material type isn't really useful (or possible) because the heaviest components of most aircraft are composed of multiple materials, and not all aircraft are built of the same materials.
The heaviest component of most airplanes is the fuselage. This is predominantly aluminum, but possibly composite in newer aircraft (Cirrus SR-22, Boeing 787), and some aircraft have multiple materials used (e.g. Mooneys have an aluminum skin, but a steel frame/cage, and "tube-and-fabric" airplanes use cloth and dope stretched over a (typically steel) frame).
While the alloy (or composite) used for the fuselage is probably relatively light compared to say a car's frame & body it's usually the largest part of an aircraft, and thus the heaviest.
The number two component on an airplane is the engine (or engines) -- the engine may even be the heaviest component of some aircraft (Ultralights and some tube-and-fabric aircraft).
As with the fuselage an engine is often comprised of multiple metal alloy: crank shafts and cams tend to be steel, lifter faces are often cast iron, the crankcase tends to be aluminum, pistons are usually both (a steel barrel mated to an aluminum head), and various alloys are used in bearings and valve guides.

As an example if we look at a Piper Cub the heaviest alloy is probably steel (the fuselage tubing, crankcase, and camshaft are all steel). Number two is probably aluminum (the engine crankcase, pistons, and cylinder heads are aluminum, as are the wing ribs and possibly the spars). Number three might be wood (if the spars were never converted to aluminum), but is more likely the fabric (and dope/paint) used to cover the fuselage.
As a different example, consider the de Haviland Mosquito: The heaviest component of this aircraft is unquestionably wood (as the aircraft is constructed almost entirely of wood), and the number two item is probably aluminum or iron (from the engines & propellers).


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Identification of this control panel for a four-engine plane
While cataloguing a printer's copper plates I came across a control panel image, and I have attached it here in the hope someone can identify what plane it's from. The Lorenz blind-landing instrument gives an indication of the period.

copper plates!  wonderful!

This is almost definitely the cockpit of a Short Stirling of unknown mark, a 4-engine British heavy bomber from World War II.
The RAF Museum's website has an (admittedly low-resolution) photo that matches quite closely, as does this history website. Here's my thought process:

the placards (not just the photo's labels) are in english, so it's likely either Commonwealth or American-built
the Stirling power quadrant is a match (2 levels of 4 levers each; it's a 4-engine bomber)
engine instruments directly above throttles
the engines have boost gauges; the Bristol Hercules engine of the Stirling was supercharged
odd-shaped cutout on the right side (just above the marked Air Speed Indicator in your photo)
my second link has a photo with a matching CAUTION JETTISON CONTAINERS BEFORE BOMBS placard on the right side
the Lorenz system was used in British (and German) aircraft during WW2, but I can't seem to find any US bombers that used it.
it has a retractable undercarriage; Short's Sunderland flying boat has a lot of the panel in common, but it was wider and didn't have the goofy notch on the right side, and it obviously had no landing gear.

In short, I'm pretty confident this is a Stirling.
Other aircraft I looked up and discarded as not a match:

Avro Lancaster
Avro Shackleton
Boeing B-17
Consolidated B-24
Handley-Page Halifax
Short Sunderland
Avro Vulcan (similar throttle quadrant, otherwise way off)

jettison containers before bombs. Containers of what?

@Mazura yeah, good question. I'm guessing incendiaries — the British used "Small Bomb Containers" (SBCs) to load and drop 4lb or 30lb incendiary devices. Also possible: Wikipedia has a cited statement that "Up to six ferry tanks could also be installed within the wing bomb cells in order to increase fuel capacity by a further 220 gallons" but I'm not sure they'd label that this way.

See also the wikipedia article on the Avro Lancaster which talks about the incendiary loads / SBCs.

Thanks for that

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Should I have one hand on the throttle during engine ignition?
I'm training in a Cessna 172 for my private pilot license (PPL).
My flight instructor recommended that I keep my checklist in one hand (so that I can keep looking outside with my peripheral vision) and turn the magneto key with the other.
The other day another instructor told me that the checklist should be on my lap and my right hand should be on the throttle, in case I find the setting too high on starting the engine and I need to decrease power immediately.
He sounded like this was something very obvious and said I'll fail my checkride immediately if I didn't have my hand on the throttle.
To be as safe as possible I could put my checklist down, start the engine with the right hand on the throttle, then pick up the checklist again, but is this really what I should be doing, and if I don't will I really fail my checkride?

I think most answers will be opinion based, but I would recommend that you ask your first instructor why he feels it is more important to hold the checklist while cranking than to have your hand on the throttle.  Because I agree with the second instructor.  (And will bet most others do too...)

P.S.  I don't like holding checklists when single piloting anyways.  I would prefer they be clipped to the yoke, or on my kneeboard so that both hands are free if needed.  If workload is light just trace your way down the items with finger or thumb of a free hand.  If I am not flying and acting as co-pilot instead it's different...

Don't over think things, or you will psych yourself into making too many mistakes.

Yes hand on throttle when starting, always, except on engines with fuel injection where you have to have it on the mixture because you start on idle cutoff and move it up as the engine catches.  In any case, you shouldn't be reading checklist items during the start; you just learn what to do and do it so you can be in total control.  Back to the checklist after the engine is running and you are satisfied it's running properly on its own and you can divert your attention to other things.  Whoever was telling you to hold the checklist during the start is... well... an idiot.
I don't think you'll fail a checkride, but will probably get marked down a bit for that item.  Most checkride fails are because a series of screw-ups accumulates and drops your overall score, not because of a single item, unless the single item is something critical and screwing it up is dangerous, like taxing onto a runway with an airplane on final or making a really bad judgement call or leaving out a critical item.
When you do your check ride, you will probably be convinced at the end you failed, if you made this little mistake and that little mistake, and will be shocked to hear "you passed".  Because unless you do something that shows the examiner you're dangerous, it's the overall scoring that counts.

+1, esp. for the reminder that checklist should be treated as a checklist (that everything has been done), not a TODO list.

On my own airplane, which is pretty simple, I don't use a checklist;  I do a "flow", which is basically moving to the actual items, pointing and checking, in a standardized repetitive pattern. It pretty much as effective as a checklist once the flow is fully internalized.  The physical pattern becomes your checklist.  It works well when there aren't a lot of life or death items.  Gliders do a similar thing, using mnemonics like CISTRSC. On transport a/c you generally do flows to physically check items, then get the checklist to do the challenge/response for the items you checked in the flow.

It is of the opinion of the FAA that you should, according to the airplane flying handbook

When activating the starter, the wheel brakes must be depressed and
  one hand is to be kept on the throttle to manage the initial starting
  engine speed

This is merely a suggestion, there is no hard regulation on the books saying you should. Although if something were to happen as a result you could be in violation of § 91.13 Careless or reckless operation.

That is what kneeboards are for.  I'd be surprised if you haven't seen one, but just in case, here is what I am talking about:

When you clip the checklist to the kneeboard, you are holding it.  When I fly, the only time I actually touch the checklist is to turn it over (when it is two sided) or to point at items as I do them.
As to whether you should hold the throttle, I will give the rather unsatisfying answer of "That is what I was always taught."  That said, an examiner is going to be following the Private Pilot ACS (assuming you are in the US) and is going to be evaluating you on those items, of which, keeping your hand on the throttle during engine start is not a part.
Personally, my hand stays on the throttle during all parts of a flight that don't involve cruising.  IOW, Engine start, taxing, takeoff, climb, descents, traffic pattern and, of course, landing.  YMMV as it probably also depends on the airplane, whether you have an autopilot, etc.

My instructor wanted the checklist pulled out of the kneeboard and held at eye level so that I'll realize mishaps like inadvertently releasing the brakes and taxing into something. But like @Zeus says I guess i should have been using the checklist after the procedure in the first place.

Isn't the best way to avoid "inadvertently taxying into something" to be looking out of the windows, not at a checklist held up in front of your face at eye level?

@RyoMiyajima Surely in such a situation you'd feel the airplane moving, and can reapply the brakes, even if for whatever reason you are looking down at that exact moment?

I'd like to answer by offering a counter-question for you.
I think we can agree that the seconds surrounding the engine start is one of the few really critical moments in getting an airplane off the ground. Sure, the rest is important as well, but you can usually afford to lose a few seconds during, say, the magneto check, or while lining up on the runway for departure.
If we can agree on that, then the question for you becomes: does holding the checklist in your hand during engine start somehow help you start the engine in a safer manner?
Maybe, in some roundabout way, it can be argued that it does. But in this specific case, there seems to be a much more direct argument that can be made that holding the throttle will help you react much more quickly in case, say, it's mis-set and the plane lurches forward when the engine takes.
(You probably should verify that the throttle is set to idle, or very close to idle, before you begin starting the engine, but this is part of the belt-and-suspenders attitude you'll see a lot in aviation.)
When in doubt, always refer to an approved checklist. If the checklist doesn't say, then make a judgement call on what's more likely to make an emergent situation easier to handle, or what is more likely to improve aviation safety, and go with that. If you're having trouble working that out, talk to your instructor. I really recommend getting into the habit of not asking just what to do; rather, ask why to do it in some particular way. You're paying for your instructor's time, and their experience in these matters; as long as you're learning, they can handle the occasional "dumb" question.
Also, the checklist probably calls for you to somehow verify that the engine is healthy immediately after starting it. In the airplane I fly, the immediate check is for the oil pressure to be within limits. It pays to read ahead a little before starting the engine, so that you can proceed immediately with those immediately-after-start checklist items. The checklist is a tool to help you remember each and every step, but you are allowed to read ahead when doing so is beneficial. Just don't forget any of the steps.


text:
Is it recommended to get a life raft for short overwater operations?
I'd like to fly to Santa Catalina Island (AVX) from the mainland around Los Angeles.  There is a portion of this overwater flight where my Cessna 172 will be beyond gliding distance from land.  I know that people usually do this flight with only life jackets, but the water is about 64 degrees F (18 °C) right now and I'm pretty sure that if I needed to make a forced landing in the water I may have hypothermia before rescue arrives.
Is it recommended to take an aviation life raft?  They're pretty expensive - they start at US$1000 for a two-man raft.  I see that raft rentals are available, but that's kind of a big pain, especially because they are going to be shipped from some other location and there is the possibility of needing to reschedule the flight because of weather.
What are the recommendations of authorities? Is there any alternative equipment that would be as effective in this scenario?

Have you thought about the size and weight of it, whether you are taking passengers or not? Could you manhandle it out of the airplane after ditching?

Maybe this should be reopened and closed as a duplicate, not opinion-based.  I would expect nearly identical answers.
https://aviation.stackexchange.com/questions/42236/when-is-flotation-gear-legally-required-for-pilots-and-passengers-on-a-non-comme

I don't think it's a duplicate. That's about legality, this is about best practice.

For interest - here is a helicopter marine immersion simulator intended for training oil rig crew prior to flights to platforms off the African coast. This is in a factory in China. When installed you get dropped in a swimming pool and optionally in the dark. I had a (dry) run. Even dry it was surprisingly scary. Helicopter immersion simulator The man in the orange shirt is the client.

@DJClayworth welcome to the Aviation Stackexchange community.  I would have thought the same thing 2 years ago.  It is a clear precedent here that marking a question as duplicate is actually less about the question being asked and more about the answers it would generate.  So based on the history of moderator judgements and meta questions addressing it, this would be a duplicate because it would generate the same answers.  Anything purely opinion-based is really not meant to be asked.

Does this answer your question? When is flotation gear legally required for pilots and passengers on a non-commercial flight in a small airplane over water?

@RyanMortensen  Thank you. The answers here are very different to the answers on your linked question, so I think it's not really a duplicate.

If you are really scared of the water... https://seaplanesoflosangeles.com

There's a nice video from Aviation 101 on flying to Catalina. No mention of a raft, but they do wear manually inflated life vests. https://www.youtube.com/watch?v=CQ3LGEsKb4Y

I'm not a pilot, but an offshore sailor.  The only objection you raise is price.  I can't put a price on your life.  I have read more than a few cases of ships lost at sea which didn't have appropriate safety gear (EPIRB, life raft) because "it was expensive" states the surviving relative.  Yet they have expensive "toys" like a $500 Yeti cooler.  The yacht (or plane) itself is expensive.  It's not a fun expense, but arguably you'll spend less time worrying if you have the proper gear.  On the other hand, if you need it and don't have it, you won't regret it for very long...

@Jason the main objection is it's expensive and useless in the situation described.

@John K, Respectfully, I disagree.  A fire extinguisher is useless in many situations.  Seatbelts are useless in head-on collisions over 80MPH.  Finding a situation where a safety device is useless is often a subconscious rationalization for a decision we have already made, but don't feel good about.  Sure, the life raft probably IS useless in most situations.  Would you still decline to take the liferaft if it was free?  Why?  At the time of this comment, only one person has even mentioned space or weight.

@Jason no worries but if you ditch in a high wing airplane like a 172 there is no way you will be able to get out while extracting a life raft.  The airplane will sink like a rock and it'll be maximum effort just to get out.  If you tether yourself  to the raft it'll just end up pulling you under as the airplane sinks.  You're going to be in the water 30 min max before a CG helicopter gets there.  A Mae West is all you need.  Even there, you have to be careful not to inflate it until you're out.

@PeterMortensen I approved your edit because it was mostly useful, but you don't have to link everything to Wikipedia. Especially Los Angeles really does not need a Wikipedia link in this question. Also see Do we really need to reference everything to wikipedia? on Meta.

I used to be a bush pilot flying Cessna 180s on floats. If you ditch in a 172 on wheels with a life raft in the back seat, it's going to flip inverted when it contacts the water and start to sink immediately, and getting your own carcass and your passenger out of the thing without drowning will be enough of a challenge.  Forget about trying to pull a life raft out of the back seat of a sinking inverted 172 after you just escaped.  It's gone.
If you are that wary of overwater flight, the normal practice, for things like trans Atlantic ferries, is to wear an immersion suit. With the water at 64F, you could get by on a warm weather immersion suit or a sailing dry suit plus life jacket, but even without, it takes quite a few hours for 64F water to kill you, and the Coast Guard is going to be there within 30 min.
In any case, a 172 has an L/D of about 9, which means from 10000 ft you can glide somewhere around 17 miles.  At mid point between between Long Beach and the island you are less than 15 miles from shore, so there's really no need to worry about ditching in the open ocean, unless you want to do the flight at a couple thousand feet.
Even if you only climb to 5000, you could glide to a few miles of either shore.  And the actual "risk exposure" time of the engine spontaneously blowing up in your face without warning, while out of gliding distance of land, is only a few minutes. The probability of this happening, that is the engine doing something like throwing a rod suddenly, in that little time window, is a fraction of the probability of driving your car off a bridge into the water on your way to the airport.

The additional advantage of height is that the rescue can start before you're in the water.

To amend John K's excellent answer:
In the unfortunately unlikely event of you being able to get the life raft out of the sinking Cessna, you'd be soaking wet and operating it would be very hard. If you manage to inflate it, and mind you, outside the plane, your a**e would be freezing anyway.
For the life raft to be useful, given evacuation goes ok, you'd have to be very proficient in using it. So where do you practise... and when...
I'd absolutely ditch (pun intended) the idea of the life raft. Your best life insurances are:

Altitude. Fly as high as safe considering hypoxia. If something happens, you have good gliding distance, help has time to react and you can troubleshoot
Keep in touch. File a flight plan and stick to it. Talk to ATC so they know where you are.
Immersion suit. If possible, get an immersion suit (and wear it). It's a bit uncomfortable, but you can just wear it waist high, and if shit or something else hits the fan, get it all up. Practise this in the plane. Wear a warm midlayer.

I've tested an immersion suit in 32 °F (0 °C) water. If you have enough midlayer, it's actually quite comfy. Your face is freezing, yes, but other than that, could have probably spent hours floating in the hole in the ice.
A quick search shows that for 1000$ you can get two Solas suits + more than enough midlayers.
note: I originally used the term flotation suit, dug up from dark depths of my english-as-a-third-language brain. Fixed that now, thus some earlier commentary refers this

I once attended a talk by a guy who was involved in the Cirrus that ditched off Greenland when (they think) the engine breather froze over and made the engine dump all the oil out the prop seal.  They guy used his temperate/tropical immersion suit, more or less a sailing dry suit, even though it was winter.  A helicopter just happened to be only about 45 min away in south Greenland checking on a remote radio facility, and rushed to the site.  They found him dead of exposure floating about 1/2 mile offshore.  If he had a proper winter immersion suit he'd have been fine.

The one I've used is only a shell. There is no insulation in the suit itself, you wear midlayer(s) according to the conditions outside.

... and the shell itself really insulates absolutely damn nothing. I've tried that too

The cold water ones have pretty thick shells and make you look like Gumby.  You can't really fly with it all the way on, but have to have it ready to go, so they are worn rolled down to the waist during oceanic ferries.

You are referring to the neoprene ones right? The thick ones are really clumsy yes. But you can get a thinner one and wear a midlayer or two under it. I would recommend this, because while thick neoprene is a good insulator, it does not transfer or even out moisture in the suit at all. You' ll eventually build condensatuin in certain part. Layered clothing is the way to go in any cold situation, land water, air.

DO NOT wear any type of Flotation in an aircraft except a manual air inflation system, if you are still inside when the cabin goes under the water it will PIN you to the top [ceiling/floor depending on how you land] and you may be unable to escape]

You are absolutely correct. But to be clear, there might be a translation issue here, the suits I'm referring to have no active components. They float you with the amount of air trapped inside the suit once you have sealed it. Same applies for the ones (I presume) @JohnK is referring to, with the added flotation of neoprene in his type. Self inflating flotation devices are a big no-no, and manual ones have to be correctly set up, so that unintentional triggering is impossible.

just FYI, there's a typo!  in the very first phrase "unfortunately" should be "fortunately".  (It is "fortunate", that, it is "very unlikely".) cheers @Jpe61

No @Fattie it's unfortunate that it's unlikely you would get the raft out of the plane. I do not wish it to be unlikely, but unfortunately it is.

Fall in the water with your shoes on w/o an immersion suit and you die. (The Great Lakes Surf Rescue Project). My brother worked on The Odyssey. Out past the break water it's not search and rescue, it's recovery.

hi @Jpe61 ! I do see what you mean, but it's a bit unusual to phrase it that way. In shoirt ("unfortunately!") in English "In the fortunately unlikely event .." or "In the happily unlikely event .." is a pretty standard formulation in English, so it comes of as that pattern!  Anyway cheers!

Immersion suits can be a life saver. Or a killer. As with a life raft, don't use them without training. Unlike a regular diving suit (also neoprene), Immersion suits are overly large, to adapt to different sizes of people and clothes. They trap air. If you don't know how to push the air out of the suit upon hitting the water, you risk getting stuck upside down in the water with a air pocket at your feet. Kills you faster than hypothermia. I'm a sailor and I've seen a fair share of people in this position during pool training. This might help: https://youtu.be/Odpw0cwkbcA

I can't speak on whether or not to bring a life raft, and others have already posted their views on that.
I can add a few more items to consider in addition to what others mentioned:

Don't forget to wear a portable EPIRB (Emergency Position-Indicating Radio Beacon).  They are available for purchase and for rent.  One can be attached directly to you; make sure it also has a sturdy backup lanyard in the event it tears off of you.
Attach a flashing water-activated portable strobe to you.  Don't assume you will be found while there is still daylight.  Note that some have strong magnets in them.  If that could affect your flight instrumentation, make sure it does not have a magnet.
Bring a signaling mirror, preferably one with a small hole in the center to help with targeting.  Practice with it ahead of time.  Make sure it is attached via a lanyard.
Bring self-launching waterproof flares.
Bring a waterproof portable VHF radio.  Test it before going anywhere.  Learn how to use it and change signal strength on it blindfolded.
Research cell phone service in the area, and bring a waterproof cell phone that has the best chance of having a signal.  Pre-program it with anyone you may need to contact for an emergency.
Bring ocean rescue dye.  When released, it causes the water around you to change color; this makes your whereabouts much more obvious from the air, and from larger ships.
Decide on a plan on how you are going to deal with sharks, should they be the first to respond.
Study shipping lanes in the area and evaluate whether you want to be near them or far from them.  A large ship may be able to rescue you if they happen to see you, but you have to guess if they will actually see you.  Many large vessels have no way to quickly stop or maneuver away from you.  If you get hit by one, it will likely be fatal.
Plan for the possibilities of being near your aircraft in the water or away from it.  Understand the advantages and disadvantages of each possibility.
Include a fire extinguisher that is rated for any elevations you might be encountering.
Consider bringing a portable paddle.  They are very lightweight, inexpensive, and not very bulky.
Bring calories with you (such as energy bars) as well as some fresh potable water.
If you have any required medications, include them in your rescue kit.
Include basic first aid supplies that will work when wet.
Wear highly visible colors like bright red.
Bring a plastic emergency whistle that is specifically designed for ocean rescues.
Equip yourself with a high-intensity compact waterproof flashlight.  One that has adjustable focus is a bonus.
Bring a sharp multi-tool that includes scissors and a knife.  If it has pliers too, that's a big bonus.
Waterproof matches.  They are lightweight and take up almost no room.  I honestly can't think of a reason that you may need them, but I think it's worth mentioning.  Don't bring a lighter that could explode at altitude or from excessive heat or pressure.
Naval emergency flag (made of flexible plastic).  Another item that I can't think of a reason you would need, but they are compact, lightweight, and inexpensive.  They are orange with a black ball and black square, and look like this:

Metallic emergency blanket.  In addition to providing warmth, they can be used for signaling.  They weigh almost nothing, take up almost no room, and are very affordable.  With the right training, they can also be used to help make potable water.
Swim fins that will fit over whatever you plan on wearing (discussed in other answers).
Personal Flotation Device (PFD). Every real PFD has an official Type.  Learn about these Types, and decide which is best for you.  Also evaluate the benefits and drawbacks of inflatable PFDs.  If you consider a self-inflating PFD, ensure there is no risk of it self-inflating (or exploding) due to atmospheric changes at altitude.
Throwable flotation device.  In addition to a wearable PDF, having a throwable PDF is always a good idea.  They add more buoyancy and act as a backup.  They can also double as a seat cushion.
Visual correction and protection.  Do you need glasses to see?  Plan for how to deal with that if you wind up in the ocean.  Also, have the necessary equipment to deal with the possible intense brightness and glare of the open ocean.
Swim mask.  For some, the salt in the ocean causes temporary blindness.  A swim mask or swimming goggles can help prevent this from happening.
Make sure you are comfortable being in the cold and turbulent ocean and can swim in the conditions you could possibly encounter.
Sunscreen.  If you do wind up in the water, you don't know how long you'll be out there.  Depending on the currents, you could be moving fairly rapidly from where you first went down.  Sunscreen can help prevent painful burns.  Something for your face and for your lips is ideal.
Attach SOLAS reflective tape to as many things as possible, including your legs and your hood.
If you are planning a round-trip, remember that the weather conditions returning may be very different than the conditions when you leave.  Don't go up if the conditions are questionable.  It's not worth it.
Contact the people who will be responsible for your possible rescue and ask them what they recommend.
Contact others who have made the same journey and ask them for recommendations.
File accurate flight plans for both legs of your journey and make sure you follow them.  Try to transmit details of any changes before you deviate from your plans.
Maintain contact with others during your trip.

Note that although this might sound like a lot of physical items, all of these items will fit inside a backpack-sized waterproof bag.  The bag should be well-organized and designed to be accessed while you are stranded in the potentially turbulent ocean.  Opening the bag should not result in everything floating away or sinking.  The bag needs to contain appropriate floatation devices so it does no sink, and possibly provide added buoyancy for you.  The bag should be a highly visible color and have some SOLAS tape affixed to all sides of it.
Well before take-off, attach any appropriate devices directly to your person.  Position your rescue bag purposefully and intelligently.
Note that although I have so far avoided dying, I do not consider myself to be an expert.  Collect data from multiple sources.  Don't rush.  Think through it and plan ahead.

There seems to be some good general survival advice here, but not much if it is relevant to the question. Some of it seems excessive for an aircraft flight that never goes more than 15 miles from land. We generally try and stick to direct answers to the question.

This is definitely an overkill considerin the question. Good advice generally speaking, but for example to take a cellphone as a safety device in case of ditching in cold water is hardly good advice.

I agree that it's overkill for this question. After composing it, I almost chose not to post it. But I figured maybe it would be of help. Regarding the cellphone, I have no idea why "Jpe61" claims it is "hardly good advice" without providing any reason at all. That's actually one of the most important items if you are within range. I personally take a waterproof rescue cellphone with me for almost all journeys. Cold water doesn't harm it. I regularly put it in a glass of ice water to demonstrate its resilience. And I've had sufficient signal to send SMS & sometimes voice in surprising places.

In item 25, should that be PFD? Also, for item 30, is reflective tape on moving legs likely to look like a fish in distress, i.e. easy food, to a shark?

A self-inflatable pfd sounds like a terrible idea.

Yes a self.inflating PFD is a very bad idea for a plane. If water comes into the cockpit then it inflates and impedes your exit. That's one reason why airline PFDs aren't self inflating.

the site's most wonderful full-monte answer!! :)

@Jpe61 what did you mean by your comment about the cellphone???  you'd easily get reception in the area described, and nothing is more useful than a cellphone.  they work fine in the cold, assuming you have it in a 2-cent plastic bag ??

Operating one in freezing cold water is far from easy, try it. In a matter of seconds your hands are numb. I have to admit I'm not familiar with cellular reception in the area of the particular  body of water  in question, but as a general advice I would not recommend relying on a cellphone at sea (or lake). You are very quickly below radio horizon and / or out of range when you are in the drink. You claim getting reception in surprising places, is swimming miles and miles from shore such a place?


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What's the profit margin for airlines between fuel cost per seat price per seat to the customer?
I understand that there are other costs that go into the full price per seat, like maintenance, crew ect., but all I am asking about here is fuel.

There are either too many possible answers, or good answers would be too long for this format. Please add details like airplane and location to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.

This also varies a lot in time. The price of a barrel of crude oil has ranged from under $20 to over $140 over the last 20 years. Also you're asking for the profit margin (in the title) and then just the fuel cost (in the body).

Fuel price varies, seat price varies (in the same aircraft), some seats are not sold, engine efficiency varies. That's a lot of approximations to be done. In addition profit is determined by all costs, airlines are unlikely using a specific uplift on the fuel line of their cost cases.


text:
Can a flow which is initially supersonic, become subsonic without a shock wave?
I am doing my college project in which air is first accelerated to supersonic  conditions in a nozzle. Then it is added into slow moving subsonic air. I see that my flow becomes supersonic and then subsonic but I don't see a shockwave. All this is done on Fluent using various 2 equation models.

Yes, it is possible . The shockless transition from supersonic to subsonic. It has been tested both experimentally and numerical solution. Read this AIAA Paper.
But in your case I would suggest you to be a bit cautious and recheck your mesh and boundary condition in CFD solver.


text:
What is the order of Reynolds number inside the Compressor at cruise conditions?
I am doing a CFD study on a probe that will be installed inside a compressor of a civil aircraft for my final year project. I need to know the Reynolds number inside a compressor at cruise conditions. Probably, if somebody has its variations along all the stages it will be really helpful. HPC /IPC/LPC any might do? I may also need the reference length chosen (which is usually the chord).
Thanks a lot in advance
Abhishek VERMA


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Why can't a plane flying due west just hover in the air and wait for the destination country to arrive?
Since the earth is rotating, why can't a plane that is flying from say, Perth to Johannesburg, just hover in the air and wait for Jo'burg to arrive underneath?

When you jump in the air, does the earth rotate under your feet? Can you put your car in neutral and "let the earth move your car"? Air moves with the earth too...

Well, in a certain sense it does.  But it has to run its engines, or it would be blown eastward by the air that's rotating along with the Earth :-)

@jamesqf No it doesn't. What happens when you launch a lighter than air balloon in no wind?  An aircrat needs engines to produce enough speed to gain lift since it's heavier than air.

@Simon: The balloon is carried eastward by the rotating air, of course.  Lift is a separate issue: suppose you had a dirigible: with no power, it's carried with the wind; with sufficient power (and ignoring structural issues) it remains stationary in a celestial reference frame while the Earth rotates under it :-)

@jamesqf It's not "carried" or blown anywhere. There is no force acting on the balloon with no wind other than upwards as a consequence of it rising. When the balloon is on the ground, it is doing 1000mph. When you release it, it is still doing 1000mph. Only if there is any wind or some other force will that change. The Earth, the balloon and the atmosphere are all moving at 1000mph. A balloon in zero wind, will not move laterally. Newtons 1st.

@Simon: Now that depends.  In a frame of reference fixed to the stars, the balloon, like the air and ground, is moving at about 1000 mph (if you're at the equator).  If you run engines to cancel that movement WRT the fixed stars, you will move WRT the air and ground.  It's all in how you look at it :-)

@jamesqf Please take it to Physics.SE. There is no such thing as "fixed stars",  all of space is moving.The Earth is not an inertial reference frame and the fact remains that if you release a balloon, and there is no wind, it is not carried anywhere. It continues to move as it did before until acted upon by an external force, i.e. it moves at the same speed is the Earth surface and the atmosphere (ignoring some minor side effects).  If it's mass was such that it hovered at 10 metres and it was a closed system, it would stay there until something caused it to move.  There is no lateral force.

@jamesqf The relative speeds between the Earth, the atmosphere and the balloon are independent of any observer.  Only their magnitude varies. Conduct a quick thought experiment. Release the balloon inside a room. Does it get carried into the wall?  Why not?  The atmosphere exerts no force on the walls of the room apart from the uniform force of pressure.

@Simon you are, of course, right in this matter, though I have to give jamesqf credit for taking the OPs point of view. I think he is perfectly aware of the fact that the balloon is not going anywhere when you release it up in the air. He said "in a certain sense [the plane] does [hover]" and I agree. Say you're on the sun, and see an airplane flying west with the same airspeed the earth rotates with, wouldn't it "stand still" ? So yeah, you are definitely right, but I don't think jamesqf is that wrong when giving the OP something to think about.


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How is the term "Coast" defined for FAA regulatory purposes?
14 CFR 91.1 defines the applicability of part 91. This paragraph defines two areas of jurisdiction where certain parts of part 91 apply:

within the United States, including the waters within 3 nautical miles of the U.S. coast
the airspace overlying the waters between 3 and 12 nautical miles from the coast of the United States

By exclusion the third area is the airspace overlying waters beyond 12 nautical miles from the coast of the Unites States. Part 91 therefore does not apply in this area. The FAA explicitly states this in letters of interpretation, for example, in Di Marco (2008).
The term "coast" appears to be undefined in any readily available FAA resources.
How are we to understand this term as applied to the scope of applicability of §91? For example, would a shore of one of the Great Lakes—Lake Huron for example—be considered a "coast" for this purpose? To apply the question more specifically, would a pilot be required to comply with the 250 knot rule of §91.117 if below 10,000 ft while 15 miles off the US shore over Lake Huron.

I don’t know. But, wouldn’t the coastline of any part of the Great Lakes within the internationally accepted borders of the United States be a moot point. After all, the regs state “this part prescribes rules governing the operation of aircraft within the United States, including the waters within 3 nautical miles of the U.S. coast.” The waters of Lake Huron within our borders are therefore covered regardless of their distance from shore since they are within the United States. The word “including” just extends the jurisdiction of the US to waters outside of our border.

Ignoring regulations for a moment, lakes usually have "shores"; the word "coast" always means the sea to me. Do people talk about the "coast of Lake Huron"? Laws and regulations generally only define words when they differ from common usage, or for precision. It seems likely to me that "coast" isn't defined because it's 'obvious' what it means. This could be a law.SE or even an ell.SE question, if you don't get a good answer here.

@Pondlife I agree with you. Coast, coastline, coastal waters, coastguard all mean the sea. I'm not from the US, but it seems very clear what the legislation refers to

@pondlife @ Dan Multiple regulations or codes specifically reference the Great Lakes as international waters or as having coastlines. See for example 46 USC 12.120.

Careful with that assumption, @Dan, the Coast Guard does patrol the Great Lakes, and they do rescue work on in-land lakes and rivers as well. Otherwise I agree with you 100%.

Coastline means the territorial sea baseline. In the language of international treaties like UNCLOS, the territorial sea doesn't include internal waters, regardless of their size. NOAA confirms this, notes however also, that not all US court decisions follow that view. NOAA also provides a map to view the US territorial waters & exclusive economical zone, which shows that the great lakes are neither.

Great answer - are you certain the FAA lives by these definitions? (Logic indicates they should, but that's not guaranteed.)

@FreeMan no, I just know international maritime law and answered the question from this perspective, so it might not be a full answer, if someone has some FAA specific information, that'd be of course even better.

As @Florian answers, the short answer is that we actually need to look at the term "baseline," which is the legal term used in international treaties.
The authority for FAA jurisdiction over the airspace defined in §91.1 is given in 49 USC  40103. This is shown in the official Federal Register docket of 14 CFR 91.1 which lists all authority basis for the regulation. 49 USC  40103 states in pertinent part:

(a)Sovereignty and Public Right of Transit.—
(1)The United States Government has exclusive sovereignty of airspace of the United States.

For the purposes of this code, the legal term "United States" is previously defined in 49 USC 40102 as:

(46)“United States” means the States of the United States, the District of Columbia, and the territories and possessions of the United States, including the territorial sea and the overlying airspace.

So to understand what the FAA actually has jurisdiction over, we actually need to understand what the term "territorial sea" means, so we know what the FAA meant by "coast."
In 1988 US president Ronald Reagan issued proclamation 5928 which declared that the US is sovereign over the territorial seas and defines this as the area extending 12 NM from the baselines of the United States.
This NOAA page defines the baselines as the low-tide line of water along the coast as charted on certain NOAA maps. That page also defines "territorial seas" as waters that extend seaward from the baseline up to 12 NM. I think water past that would be international waters with freedom of passage for any nationality. More specific to this discussion, that same page defines a separate term, "internal waters", as opposed to "territorial seas" :

Internal waters are the waters on the landward side of the baseline from which the breadth of the territorial sea is measured. Each coastal State has full sovereignty over its internal waters as if they were part of its land territory. The right of innocent passage does not apply in internal waters. Examples of internal waters include bays, rivers and even lakes that are connected to the sea, e.g., the Great Lakes.

So based on the NOAA sources, the Great Lakes are specifically excluded from Territorial Seas for this purpose, and by extension, for FAA purposes since the FAA authority is derived from the same basis.
In the absence of a specific FAA provided definition, these combined facts are probably the best answer to this question.


text:
SPL recency requirements after skill test
According to SFCL.160 SPL – Recency requirements an SPL holders shall exercise SPL privileges only if in the last 24 months before the planned flight they completed two training flights with an FI(S).

There is a specific exemption if the pilot has passed a proficiency check. My question is what happens if the pilot just passed the skill test for the for the purpose of issuing the licence? Does it mean your SPL does not yet meet the recency requirements until the pilot has performed the two training flights with a FI(S) after the skill test?

Typically a check flight trumps a review.  i.e. the "skill test" you mention would also count as a proficiency check and start the 24 month clock ticking.

@MichaelHall that's how I interpret it as well, but they only explicitly mention proficiency check they could have easily added an OR for the skill test. So it feels like this is explicitly omited.

You can do either point 1 OR point 2, meaning that if you do the "skill test" mentioned in point 2, you no longer need the 2 training flights with a FI(S) mentioned in point 1 (ii).
If you talk about the skill test after which you obtain the license (from student pilot to an actual pilot) - YES you have the privileges (you just passed a "skill test").
After the skill test, you have 24 months ahead with the SPL privileges!
They do mention the "or" just at the end of point 1 (ii) - or before point 2: "two training flights with an FI(S); or".
--- short explanation ---
This rule is for the case in which you take a longer break from flying (24 months at least). Because of that, you might get "out of hand" ("forgetting" how to fly) and not pilot as well as before, including some safety risks.
So you have to start flying again to "remember" or "train again" your skill. Meaning that you have to do 5h of flight + 15 lunches + 2 FI(S) flights (either with instructor or solo but under supervision) - after which you have the privileges back, and another 24 months start.
But in case you are confident that you can handle it - request a flight with a FE(S), which it is "based on the skill test for SPL", after which (if you pass) you have the privileges, without doing everything written in point 1.
In case you will not take a break - you will constantly add more and more hours to these 5 hours, more and more launches, so you will always have the requirements in the last 24 months, just remember to do the 2 flights with FI(S).

I hope this answer helped you, and if you have any questions, do not hesitate to ask!
Captain Pelican

Yes I am specifically referring to the scenario of passing a skill test after which you obtain the license (from student pilot to actual pilot). That's indeed how I see it as well, found it a bit strange they mention proficiency flight but not a skill test explicitly. Thanks for the confirmation though.

@max, But before you pass the skill test you are not yet an SPL holder, therefore you cannot exercise SPL privileges, therefore the entire section is not (yet) applicable.  Right?  In other words, "once you have passed the skill test the following recency requirements apply" is implied.

True there could be a confusion between proficiency flight and skill test, but tho.. they basically mean the same thing:) I'm glad my answered help:) And what @MichaelHall mentioned is very correct^^ you must pass the "first" skill test for the recency requirements rule to start


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Is EASA B1 equivalent to DCAM B1?
I am from Bangladesh. Bangladesh has EASA 147 approval.

Is EASA B1 equivalent to DCAM B1?
Will Bangladesh accept the license?
If I want to convert the DCAM license to EASA license what do I have
to do?
About type training, from which country should I get the training?


text:
When did FedEx acquire its current callsign and airline ID's?
FedEx currently uses the callsign "FedEx" and has the IATA and ICAO ID's of FX and FDX respectively.
Back in the 1990s they used the callsign "Express" and the IATA code was FM.
When were they reassigned the new callsign and IDs? Was it in 1994 when they changed the official name of the company from Federal Express to FedEx?

Don't forget about FedEx's feeder carriers, which have their own callsigns.

According to this site you are right, there was a previous entity called Federal Express Corporation (IATA: FM / ICAO: FDX) which ceased to exist in June 1994 (when FedEx rebranded) and gave way to the entity we now know under the name FedEx Express (IATA: FX /  ICAO: FDX).


text:
Which engine type requires the shortest take-off run: a turboprop or a turbofan?
If two fixed-wing aircraft almost identical except for the engines, one turbofan and one turboprop, which one would need less runway to take off?

Takeoff distance is much more a factor of wing loading and other factors rather than engine choice.

GdD is correct. Lots of factors go into takeoff performance; engine type being just one. That said, if all things are equal and somehow you had the engines on the exact same aircraft, I would guess that you'd also have to reduce weight on the turbofan to keep it equivalent with the turboprop, thus reducing engine size and thrust capability. At slow speed, a turboprop will generate thrust more efficiently, so my guess would be that the prop would be able to get the aircraft to takeoff speed faster and use less runway. But it would quickly get smoked as speed increased. Pure guess though.

I'm not sure that I agree with @GdD. Jets produce thrust more efficiently at higher airspeeds, while turboprops produce thrust more efficiently at lower airspeeds. All other things being equal, a turboprop should accelerate more quickly, and therefore need less runway, than a jet.

Why "requires"? I guess you wanted to ask "which engine type allows the shortest take-off run". Please clarify.

Requires because takeoff runway is a limited precious thing.

Even with similar weight, turboprop and turbofan aircraft will have different design characteristics. A turboprop will fly at lower altitudes and airspeeds, resulting in different aerodynamic designs. A turboprop also burns less fuel per hour, so it will need less fuel capacity.
That being said, we can look at some aircraft to get an idea of what the trends might be. The best example is probably the Dornier 328. It's a turboprop aircraft that seats about 30 passengers. There also happens to be a version of the plane with jet engines. This is probably about as similar as you can get in both weight and aerodynamics. According to Skybrary, the figures are as follows:
Dornier 328
MTOW 13990 kg
Distance 1000 m
Dornier 328JET
MTOW 15200 kg
Distance 1382 m
You can see the the jet derivative is a bit heavier but requires a much longer takeoff distance.
The trend is similar between other aircraft.
Dash 8-300 Turboprop
MTOW 18600 kg
Distance 1085 m
ERJ-135 Jet
MTOW 20000 kg
Distance 1580 m
CRJ-200 Jet
MTOW 21523 kg
Distance 1527 m

Everything else being equal, and for the same engine power, a turbofan will need more distance, since turboprops give more thrust than turbofans at small airspeeds. In general, and for the same power, thrust at low airspeed is higher the lower the 'disk loading' is. That's why helicopters have big rotors...

Turboprops are better for shorter takeoff. What other posters missed and that surprises me is the effect of the air displaced by the engines on the wings.
Turbofan displaced air is mostly directly thrown back while turboprops throw a large quantity of air on the wings. The air accelerated against the wing will give extra lift since it's what the wings are made for. If the plane advances at 50 knots and the turboprop accelerates the air a further 50 knots backward, some portion of the wings will see airspeed of 100 knots.
For example, an A440m can takeoff at mtow(max take off weight) within 980 meters. A 767-200 will do it in 1900 meters. Those planes are within 2 tons of each other so that should give a rough idea.

While an A400 and a 767 may have similar weights, they are designed for two totally different purposes and different operating environments. It may not be a reasonable comparison.

The A400 and 767 have completely different wing designs. This isn't a valid comparison.

For two identical airframes, one turbofan powered and the other powered by prop jets, it's going to be a matter of the total available thrust from each as we as the thrust to weight ratio of each engine installation.  The lighter the engine / propeller and the greater the thrust, the shorter the takeoff roll will be by Newton's Laws
F = m*a
Here, the total force propelling the aircraft forward is the engine thrust force Fe subtracted from the sum of the Aerodynamic drag forces and wheel friction.
F = Fe - Da - Df
So a becomes
a = (Fe - Da - Df)/m
And the time of takeoff roll from standing start using basic kinematics.
Vr = a*t
And the total ground roll as
L = 0.5*a*t^2
In the real world, jets are designed for different cruise and mission profiles than turbopropeller aircraft, which requires the use of different airfoils and wing planforms.  Typically swept wing aircraft have higher stall speeds and consequently higher Vr than do rectangular or tapered planforms usually found on turbopropeller aircraft.
The comm nets made about the section from Aerodynamics for Naval Aviators are interesting.  This effect would be most noticeable on a fixed pitch propeller but minimized with a proper constant speed propeller which can keep propeller efficiency around the theoretical maximum of 85%-88%.
One advantage which a turboprop will have - at least for a tractor configuration - is that the prop wash over the wings creates additional lift, which can reduce Vr.  Propwas over the tailplane can provide additional elevator authority as well, reducing the takeoff roll here.

I did not downvote, but the quote "Everything should be made as simple as possible, but no simpler." seems applicable.

This doesn't take into account the dynamic variation of thrust throughout the takeoff roll for propeller aircraft as opposed to the more constant thrust of a turbojet aircraft throughout the takeoff roll. See Aerodynamics of Naval Aviators, p 185.


text:
What equation describes the relation between engine thrust and EPR?
What is the formula for engine thrust as a function function of engine pressure ratio (EPR)?
If the EPR is lower than 1, is the engine producing thrust? For example during descent, when the engines are in idle power.

If the engine is running it is producing thrust. Even at idle power, the engines are producing thrust, how much depends on what engine.

@Ron Beyer  It At 'idle power', with little or no torque applied, a propeller will absorb power from the relative wind, producing drag, that might be seen as a 'negative thrust'. The same will happen with the fan of a turbofan or –in general– at any 'actuator disk'...

I suppose if the "relative wind" was equal to the thrust of the fan or propeller, it could be zero thrust. A B777 engine which produces about 115,000 lbs. of thrust at full power, still produces about 4,000 lbs. of thrust at idle.

@xxavier The thrust can't be negative, otherwise the aircraft would move backwards at idle sitting on the tarmac. Quite a few aircraft, props and jets included, produce enough thrust at ground idle to move the aircraft forward at a good clip. The drag in flight is noticeable because it is a difference in velocity, most aircraft can't fly (level) at idle thrust, but there is a positive thrust there, it just isn't enough to maintain level flight. Same as if you just throttled back to 25% or some other low thrust value.

@With enough headwind, a prop aircraft at idle will roll backwards on the tarmac... Please see this: http://imgur.com/TlztzL4  In both cases, the propeller has the same headwind, but in the upper figure the revs are high enough to give a positive thrust, while in the lower sketch the revs have dropped, and the thrust becomes negative...

EPR < 1 means the engine is producing more drag than thrust.  It may be producing some thrust, but the drag is greater.

NASA has a very website with a turbojet simulator that allows you to play around with different settings and see how the engine responds: Engine Sim.  If you go to this site and play around with the app, you can easily see that thrust is more or less proportional to EPR.  By "proportional" I mean if you double EPR, you double thrust.  Very close to idle it deviates from this behavior, but above idle it is close.  You'll also see that EPR is just one of many parameters needed to calculate thrust.  i.e. at EPR=2 at sea level static is a very different thrust than at 40,000 ft and Mach 0.8.  But, all else being equal, thrust is linear with EPR.
Now, why should that be... well, there is a lot of math involved.  On the same NASA site, you'll find a tutorial on calculating thrust (Turbojet thrust tutorial).  They don't actually show the derivative of thrust with EPR, but a lot of the basic math is there.
Now, all of the above is valid for a single spool turbojet engine, which basically nobody uses anymore.  Everything is a turbofan.  For a turbofan, there are now multiple different exit pressures to think about (i.e. both the fan exit pressure and the core exit pressure). Rolls-Royce uses a modified EPR for their turbofans, which takes both fan exit pressure and core exit pressure into account.
This article also has some more details about EPR that you may be interested in: Cockpit Design: EPR v/s N1 indicationhttp://theflyingengineer.com/flightdeck/cockpit-design-epr-vs-n1-indication/

How do you run EngineSim? The page just displays text for me.

It is a Java applet.  you may not have Java installed or there may be a problem with your Java setup.

Oh, apparently Chrome dropped Java support in 2015.

For anyone else having trouble, I made it work using Firefox ESR (32 bit): https://www.mozilla.org/en-US/firefox/organizations/

I'm heavily cribbing from Boeing's "Jet Transport Performance Methods" here, so hold on to your seat...

F = m· (V2 – V1)
where m· is the gas flow rate, mass per unit time
V1 is the initial velocity of the gas
V2 is the final velocity of the gas
Let’s re-write equation 3 in a more complete form:
Fnet = [(m·core air + m·fuel) × Vcore exhaust] + (m·fan air × Vfan exhaust) - (m·air × Vairplane)                                       Note that the force is
now called Fnet, for net thrust. What are those terms in
parentheses? The term (m·air × Vairplane)is the momentum per unit
of time of the air being taken into the engine.  The term [(m·core
air + m·fuel) × Vjet exhaust] is the momentum per unit of time of
the gas leaving the core of the engine. Notice that we are now
accounting for the fact that the mass flow of the exhaust is greater
than the mass flow of the inlet, because fuel has been added to the
intake air.  Finally, the term (m·fan air × Vfan exhaust)is the
momentum per unit of time of the air leaving the fan stage of the
engine. The net force, which is the thrust produced by the engine,
is the algebraic sum of these three terms, which is the rate of
change of momentum of the gas as it passes through the engine.
If we considered only the first two terms, the exhaust flow, we would see only the force created at the fan and the exhaust nozzle.
But this is only half of the story, because we must remember that the
flow of the air entering the engine also has momentum and the useful
work that the engine is doing is the difference between the two.

Note that m· is "m-dot." The dot should be over the letter "m" but didn't copy well from the original pdf. I bold-texted the part about force created at the fan and exhaust nozzle, because I think that's what you're measuring with EPR. Again, from the JTPM textbook:

This stands for engine pressure ratio. It’s the ratio of the gas flow
total pressures measured at two specific points: at the entrance to
the exhaust nozzle (station 7) and at the inlet to the fan and
compressor (station 2). EPR is defined simply as:
EPR = Pt7 / Pt2
where Pt2 is the total pressure measured at station 2 Pt7 is the total
pressure measured at station 7

Hope this helps. Just a little math, but I highly recommend the whole book.

We have formatting here that can help with the equations but this doesn't seem answer the question.


text:
How is the camera positioned for these plane-to-plane Schlieren images of shock waves?

These two popular press articles discuss the use of schlieren photography to image shock waves of jets during flight using a special schlieren camera on a third plane.

Gizmodo: NASA Captures First-Ever Images of Intersecting Shockwaves From Two Supersonic Jets
Ars Technica: NASA visualizes supersonic shockwaves in a new, awe-inspiring way

NASA's Glenn Research Center page on Schlieren photography is instructive but doesn't give a clue how this is done. Where is the camera relative to these target aircraft, and what's behind them?
This NASA page shows a diagram of traditional Schlieren photography but in that case a special light source is behind the plane, and the present photos are "in the wild" rather than in a laboratory setting.

I agree that the specifics of the question have to do with light, optics, etc., but the subject matter is clearly of interest to the aviation community.  As such I believe the applied tags are appropriate, and that it should remain here.  Having said that, this looks more like transonic than true supersonic to me.

Where is the camera relative to these target aircraft, and what's behind them?

Straight from NASA themselves:

NASA flew a B-200, outfitted with an updated imaging system, at around 30,000 feet while the pair of T-38s were required to not only remain in formation, but to fly at supersonic speeds at the precise moment they were directly beneath the B-200

and (alternative link)

Let us continue this discussion in chat.

I thought you might enjoy the following sequence of images :-)  https://www.instagram.com/p/CF7lRLoJBfH/?utm_source=ig_embed oh, this too https://twitter.com/johnkrausphotos/status/1314212540453285898

Supplementary answer:
As the question mentions this NASA page shows a diagram of traditional Schlieren photography and it's the idea I had in my head. I assumed you'd need a carefully prepared light beam and couldn't figure out how this was done.
Than's to @ymb1's comment, here are some slides from the NASA Armstrong Flight Research Center presentation Flow Visualization of Aircraft in Flight by Means of Background Oriented Schlieren using Celestial Objects and a technology licensing announcement from NASA: page and pdf.

This invention is an imaging method that requires very simple optics on an airborne vehicle, a camera with an appropriate lens, and an area on the ground that provides visual texture. The complexity with this method is in the image processing and not as much with the hardware or positioning, making Background Oriented Schlieren (BOS) an attractive candidate for obtaining high spatial resolution imaging of shock waves and vortices in flight. First, images are obtained of a visually textured background pattern from an appropriate altitude. Next, a series of images are collected of a vehicle in flight below the observer vehicle and over the same spot on the ground that serves as a background pattern. Shock waves are deduced from distortions of the background pattern resulting from the change in refractive index due to density gradients. The invention requires special software to create the schlieren images. The schlieren image is a contour plot of a two-dimensional data array of measured distortions, in pixel units. The results are used by researchers to help understand the flow phenomenon and compare to computational models.

Basically the camera takes two photos of a area with a complexly textured surface, one without a supersonic wake, and one with. Then pixel-by-pixel they calculate a tiny deflection of the image caused by refraction.
This is not an interferometric technique! It's similar to taking a photo of the bottom of a pool of water when the water is calm, then taking a second when the water has ripples and the bottom is refracted, then throwing the two images into a computer program to calculate what surface would have caused those wiggles in the image. If the bottom of the pool were blank, there's nothing to see.
In the earlier work the NASA group used the Sun as the textured background. They used a special filter that produces a highly granular image as the background, then shot the target planes upwards from cameras on the ground. The filter's passband is unrelated to schlieren imaging, it simply made the Sun appear granular.

Updated camera testing on the ground, screenshot from NASA Supersonic Flights Validate Flightworthiness for Future Schlieren Imaging

In the most recent image, they went back to using a highly patterned area on the ground as the background.
This means that the camera plane had to fly over and photograph the same bit of ground twice, from the same position in the air.
Once with the target panes and their wakes, and once without the planes to get an undistorted, un-refracted image for comparison.
This is why all three planes had to be in the right place at the right time, rather than the camera plane had to be in the right place at the right time to catch the other two; the shot had to line up with a certain, preselected section of ground.

One of the greatest challenges of the flight series was timing. In order to acquire this image, originally monochromatic and shown here as a colorized composite image, NASA flew a B-200, outfitted with an updated imaging system, at around 30,000 feet while the pair of T-38s were required to not only remain in formation, but to fly at supersonic speeds at the precise moment they were directly beneath the B-200. The images were captured as a result of all three aircraft being in the exact right place at the exact right time designated by NASA’s operations team.

Thanks to @Federico for finding and linking to this video!

Since they are measuring a two-dimensional displacement field, in a similar way to an optical flow measurement, they get a vector field rather than an intensity field for traditional schlieren imaging. That means they can play with the gradient in new ways.

Left: Schlieren image dramatically displays the shock wave of a supersonic jet flying over the Mojave Desert. Averaging multiple frames produce a low-noise picture of the shock waves. Right: Horizontal gradient reveals tip vortices from the same image set.

more: https://www.nasa.gov/mission_pages/lowboom/videos

@ymb1 your pdf is excellent! It's late here, please feel free to write up an answer based on it. If not I'll add some of that to my answer. BOSCO uses the Sun as background. I'll start learning about the image processing next, but not in this SE site. Thanks!!

@ymb1 revised again, thanks again for the links, I believe I understand the basic idea behind image processing now. There's probably a lot of smoothing and low-pass filtering that I don't want to know about to completely remove artifacts from the ground, but it seems to be based on a two-frame optical flow-like calculation.

The only ground artifacts would be from featureless areas, or moving objects like cars -- otherwise the refraction image is totally computed (it shows the distortion of the ground, not the ground itself), and the computation only fails where the T-38s block the ground.  If the observing plane was slow enough, it wouldn't require passing twice over the same spot to get the reference images.

@amI any extended area that was totally black or so dark as to be in the noise (e.g a large shadow) could not generate any information and so would also be an artifact. I like the point about a slow plane; some kind of lighter than air platform might work too, as long as you had a good chance of recovering your camera and data afterward some way.

Yes, shadows could be featureless areas.  As you hinted, there is probably a lot of dropout noise that can be fixed by spacial blurring or temporal copying from adjacent frames.

I suppose this could be done at home with a soldering iron or candle in air (or mixing hot and cold water) and some obliquely-lit coarse sand paper as a backdrop, just for fun. They'd both need to be in focus at the same time so a long-ish lens at some distance would work better than a cell phone camera.

@amI https://youtu.be/K08Gc0tKWoA from What would the density profile of this shock wave look like, roughly? I should really try what I was planning to do and reproduce that refraction.

I suggest a heat source with no optical component -- you need a reference photo without the heat source and another with, so you only want refractive effects, not illumination changes.  Also rock steady camera and background, and just focus on the background.  The hot object will give a soft transition, so try to have vertical heat flow with cold to the side[s].  Illum as you said.  With photoshop, make one photo a 50% transparent layer, then Select Inverse.  If the 2 photos were identical, they would cancel to gray.  ...

Adjust Curves (not contrast) for better range and look for more texture to show in the hot/cold transition zone.  Try terrycloth if sandpaper is too 'noisy'.  Good luck and post if it works (but don't work too hard in case it doesn't :)

@uhoh I did that using a checkerboard pattern (3x3 pixels/square) displayed on a computer monitor.

@KeithMcClary I love it! If your screen was rapidly alternating horizontal and vertical bars, then you could get a vector field.


text:
What are the costs involved with getting a 2 seat ultralight?
About 7 years ago I got my private pilots cert but I let my medical cert lapse.
Now that life is more settled I'd like to get back into flying but I want something that I can keep at home. I was thinking of a two seat ultralight with folding wings.
My questions are:

What do I need to do to get back into the flight seat
What are some good options for a 2 seat folding wing ultralight that has a few hour range
What are some hidden costs of owning a new or used ultralight

If they ever ramp up production, I'd love to own an Icon A5 which is available with a trailer option.

In what country? The United States? I thought that 2-seat aircraft could not be considered ultralights in the US.

@TannerSwett The United States. I think there's specific guidelines for ultralights to fall into the FAA reg you're referring too. I have my private pilots cert though so I don't care, it doesn't affect me.

What do I need to do to get back into the flight seat

Legally, not much. With the recent third class medical reform you dont even need to get a medical. You will need to get a bi-annual flight review to get current as well as your takeoff/landing requirements for passenger carrying as per FAR 61.57. While your bi-annual only needs to be an hour of ground and an hour of flight, if its been 7 years it will be well worth your time (and possibly an insurance requirement) to spend some more time on both.

What are some good options for a 2 seat folding wing ultralight that
  has a few hour range

Dont know much in this space so I wont comment

What are some hidden costs of owning a new or used ultralight

There is one guy on the field I fly out of who has one of the moving wing, snowmobile looking ultra lights. He keeps it in the back of another guys hanger and takes the wing off every time he stores it. With that in mind last time I spoke to him he said it takes some time to get the wing on and off and he needs to plan for that when he flys. If I remember correctly he bought his new or close to new and it was in the space of 75K which frankly is quite a bit considering you can get a really nice airplane for way less than that. The wing is fabric/composite so outside storage is a no go. You can hop around on nice days with it but its VFR only which depending on your goals can be a limiting factor.

VFR is fine for me. I just want something I can take my girl around the state in and out to some Islands on. I just don't want to spend $1,000 a flight to do it with Cessna rentals :-)

Depends on distance, for the price a used VFR only Cherokee 140 may actually cost you less in the end of the day and you can store it outside on the field. I would explore the cost of a Cessna 150/152 as well both have performance marginally better than an ultralight and are way more plentiful in the used market.

Do the wings come off of those easily? My property isn't big enough to store an unfolded 150 unfortunately. I really don't want to pay hanger fees either. My goal is to get back into the sport but be thrifty this time. I jumped into my cert without thinking about costs and it scared me out.

They do not, but a tie down at most fields is pretty cheap if you are willing to store outside. Are you planning to fly on and off your property as well or just store and trailer?

My vision was to get something that I could store on a trailer and back into the driveway. Then when I want to fly, drive it 20 min to the local airport and go.

Fair enough, A decent enclosed trailer may cost you the same as 3-5 years of a cheap tie down rental. But anyway I would look at wingspans and what kind of hauling you would need to make it a reality. Im sure there are different kinds but the one I have seen has a single piece wing that is quite large.

Let us continue this discussion in chat.

Careful though, 3rd class medical reform does not automatically mean you don't need a medical, especially if you've had a medical revoked or surrendered. This is one of those instances where he will probably need to talk with an AME.

He states he let it lapse, I did assume that meant he simply let it expire and it was not revoked or surrendered.

@Dave I did read it wrong (thought he said due to medical reasons), but if that were the case and he has a medical condition that would otherwise require a waiver, he would still need to go through that process.